In general, ceramics articles are highly desired for many applications, particularly high temperature structural applications, due to their refractoriness and high-temperature strength. However, the poor damage tolerance of monolithic ceramics limits their use. Ceramic composites like continuous fiber ceramic composites (CFCCs) are extremely damage tolerant and are materials of choice for high temperature structural applications, however, high manufacturing costs have severely restricted their use.
Low cost, readily producible lamellar or fibrillar ceramic composite structures are of interest for many potential applications. They may potentially be used for non-structural applications like catalyst supports, heat exchangers, thermal insulation, filters and many others, based upon characteristics such as their substantial surface-to-volume ratio and low density as compared to metals. Such materials also have potential application as structural materials, including high temperature structural materials, where their physical properties and microstructure may be used to distribute localized stresses and provide high temperature strength.
Lamellar and fibrillar minerals occur naturally, such as mica and asbestos, and have been commonly used as fillers and reinforcements in various composite materials. However, these naturally occurring mineral forms are not suitable for all applications (e.g. applications which require non-naturally occurring morphologies) hence, considerable efforts have been made to synthesize lamellar and fibrillar ceramic materials. Fiberglass is a common glassy ceramic material produced artificially for this purpose.
There is much interest currently in the synthesis of lamellar and fibrillar ceramics for incorporation into ceramic composites, particularly high temperature structural ceramic composites. These lamellar or fibrillar refractory ceramics, such as alumina, silicon carbide, aluminum silicate and others, currently are synthesized in a number of ways. For example, ceramic lamelli or fibers are currently formed by known methods including: whisker growth by the VLS (Vapor-Liquid-Solid) process, CVD (chemical vapor deposition) on a fiber core, spinning of polymeric ceramic precursor or gel fibers followed by pyrolytic conversion to ceramic fibers, melt spinning of molten ceramics and extrusion and spinning of plasticized ceramic powders followed by sintering.
These refractory lamellar and fibrillar ceramic structures are frequently fabricated into composite articles by combination with other materials usually designated as a matrix. These lamellar or fibrillar ceramic structures are utilized to provide reinforcement to the matrix, and are utilized because of their high strength and high elastic modulus at high temperatures.
The process of separately fabricating lamellar or fibrillar ceramic structures, particularly refractory ceramics structures, and their later conversion into bonded composites frequently includes many costly process steps. Therefore, it is desirable to develop new composite ceramics articles, and methods for making them, having lamellar and fibrillar structures for reinforcement that avoid technical and cost limitations associated with present methods and materials.